[RFC PATCH v5 5/8] ALSA: usb: babyfacepro: add S3 suspend/resume

["Ismaïl Bahloul" <i.bahloul01@gmail.com>]

Kills the stream and lets the PCM core suspend substreams (apps get
-ESTRPIPE and restart) on suspend; resume re-runs the cold init and
replays the cached mixer state.  Front-panel poll start/stop around
suspend is added by the front-panel patch, once that poll exists.

USB autosuspend itself is out of scope (already disabled at probe in
the first patch of this series) - this is S3 system sleep only.

Signed-off-by: Ismaïl Bahloul <i.bahloul01@gmail.com>
---
 sound/usb/babyfacepro/babyfacepro.c | 48 +++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/sound/usb/babyfacepro/babyfacepro.c b/sound/usb/babyfacepro/babyfacepro.c
index c15fca214..ccf3dbf36 100644
--- a/sound/usb/babyfacepro/babyfacepro.c
+++ b/sound/usb/babyfacepro/babyfacepro.c
@@ -1592,6 +1592,52 @@ static void babyface_disconnect(struct usb_interface *intf)
 	snd_card_free_when_closed(chip->card);
 }
 
+static int babyface_suspend(struct usb_interface *intf, pm_message_t message)
+{
+	struct snd_usb_babyface *chip = usb_get_intfdata(intf);
+
+	struct snd_device *sdev;
+
+	if (!chip)
+		return 0;
+	list_for_each_entry(sdev, &chip->card->devices, list) {
+		if (sdev->type == SNDRV_DEV_PCM)
+			snd_pcm_suspend_all(sdev->device_data);
+	}
+	cancel_work_sync(&chip->stream_work);
+	mutex_lock(&chip->mutex);
+	if (chip->streaming)
+		babyface_stream_kill(chip);
+	mutex_unlock(&chip->mutex);
+	return 0;
+}
+
+static int babyface_resume(struct usb_interface *intf)
+{
+	struct snd_usb_babyface *chip = usb_get_intfdata(intf);
+	int err;
+
+	if (!chip)
+		return 0;
+
+	/* The device lost its state across the suspend; re-run the cold
+	 * init and re-apply the cached mixer state.  Suspended PCM
+	 * substreams are woken by the core - apps get -ESTRPIPE and
+	 * restart (the trigger re-arms the stream).
+	 */
+	mutex_lock(&chip->mutex);
+	err = usb_set_interface(chip->dev, BF_IFACE, chip->alt);
+	if (err < 0)
+		goto out;
+	err = bf_cold_init(chip);
+	if (err < 0)
+		goto out;
+	err = babyface_restore_state(chip);
+out:
+	mutex_unlock(&chip->mutex);
+	return err;
+}
+
 static const struct usb_device_id babyface_ids[] = {
 	{ USB_DEVICE(USB_VENDOR_RME, USB_PRODUCT_BABYFACE_PRO_FS) },
 	{ }
@@ -1602,6 +1648,8 @@ static struct usb_driver babyface_driver = {
 	.name = "snd-usb-babyface-pro",
 	.probe = babyface_probe,
 	.disconnect = babyface_disconnect,
+	.suspend = babyface_suspend,
+	.resume = babyface_resume,
 	.id_table = babyface_ids,
 };
 
-- 
2.55.0